The filters to be applied must be formed in a single filter call. Set like this:
progid : DXImageTransform.Microsoft.BasicImage(grayscale = 1)
The CSS should work like the following:
.demo { background: transparent; -ms-filter: "progid:DXImageTransform.Microsoft.gradient(startColorstr = #00FFFFFF,endColorstr = #00FFFFFF) progid:DXImageTransform.Microsoft.BasicImage(grayscale = 1)"; /* IE8 */ zoom: 1; }